The Three-Dimensional Structure of Protein Molecules in Aqueous Solution

2 THE THREE-DIMENSIONAL STRUCTURE OF PROTEIN MOLECULES IN AQUEOUS SOLUTION 

The polypeptides in proteins are built of, say, a few hundreds amino acids that are chosen from the 21 amino acids listed in Table 13.1. Hence, a variety of 2H°° amino acid sequences along the chain (i.e., the primary structure) are possible to construct a relatively short polypeptide chain consisting of 200 amino acids. That is an almost infinite number. Nature has made a severe selection out of these possibilities. Yet, millions of different proteins exist, each with its own specific function. 

Local minima of the Gibbs energy (metastable states) 

FIGURE 13.2 Gibbs energy landscape of protein structure stability. (Adapted from Dill, K.A. and Chan, H.S., Nat. Struct. Biol., 4, 10, 1997.) 

Within the 3D structure, different levels may be distinguished, referred to as the secondary, the tertiary, and the quaternary structures. 

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